1. Field of the Invention
The present invention concerns a liquid crystal display device having an in-cell retarder and a manufacturing method thereof.
2. Description of the Related Art
At present, transmissive liquid crystal display devices with a wide view angle of an IPS (In Plane Switching) system and VA (Vertical Alignment) system have been popularized as monitors for various equipment and also used for televisions while improving response characteristics. On the other hand, liquid crystal display devices have also been popularized in mobile information equipment including cell-phones and digital cameras. Recently, for the mobile information equipment, models having an angle-variable display have been increased and a wide view angle is demanded since they are often observed from an oblique direction.
Since display devices for use in the mobile information equipment are used in various circumstances including from outdoors in fine weather to dark rooms, it is desired that the devices are transflective. A transflective liquid crystal display device has a reflective display area and a transmissive display area in one pixel.
The reflective display area reflects a light incident from the periphery by using a reflection plate to conduct display and, since a contrast ratio thereof is constant irrespective of the surrounding brightness, favorable display can be obtained in a relatively bright circumstance including from outdoors in fine weather to the inside of rooms. On the other hand, since the transmissive display area provides a constant luminance by using a backlight irrespective of the circumstance, a display at a high contrast ratio is obtained in a relatively dark circumstance from the indoor to the dark room. The transreflective liquid crystal display device having both of the characteristics can provide display at a high contrast ratio in a wide range of circumstances including from the outdoors in fine weather to the dark room.
Heretofore, it has been expected that reflective display and transmissive display with a wide view angle can be obtained together by making the IPS system which is known to provide a transmissive display with a wide view angle into a transflective. For example, Japanese Unexamined Patent Application Publication No. Hei 11 (1999)-242226 and its counterpart U.S. Pat. No. 6,281,952 describe a transflective IPS system.
In the transflective IPS system liquid crystal display device, a retardation plates are disposed to the entire outer surface on upper and lower sides of a liquid crystal panel, in which a liquid crystal layer is sealed between two transparent substrates but the retardation plate has view angle dependency. Accordingly, even when the phase difference between the liquid crystal layer and a plurality of retardation plate is optimized in the normal direction of the liquid crystal layer, the phase difference deviates suddenly from the optimal conditions for dark display as apart from the normal direction.
Further, the structure for the arrangement and the display characteristic in a case where a retardation plate (retardation layer) is incorporated to the inside of a panel instead of an externally added retardation plate are disclosed by C. Doornkamp et al., in Philips Research, “Next generation mobile LCDs with in-cell retarders” International Display Workshops 2003, p 685 (2003). Further, Japanese Unexamined Patent Application Publication No. 2005-338256 and its counterpart U.S. Pat. No. 7,088,409 disclose a consideration for making the transflective IPS system having an in-cell retarder so as to provide a wide view angle equivalent with that of the entire transmissive IPS system.
Since the in-cell retarder includes a liquid crystal polymer, alignment of molecules is higher compared with an existent external retardation plate manufactured by stretching an organic polymeric film. Further, Δn of the in-cell retarder is much greater than that of the external retardation plate. Further, while the layer thickness is as large as several tens μm in the case of the external retardation plate, the layer thickness can be greatly decreased to several μm when the in-cell retarder is formed by using the liquid crystal polymer.